When petroleum exploration and recovery of petroleum deposits are being carried out, it is necessary under given circumstances to inject chemicals into the well flow from the reservoir. The aim may be to prevent corrosion, formation of hydrates or deposits.
The chemicals in question here are expensive, and it is desirable, also for environmental reasons, for the chemicals to be dosed into the well stream in an amount as accurate as possible.
According to the prior art, in offshore installations, the chemicals are pumped from a floating or fixed offshore installation down to the sea floor through an umbilical, where the chemicals are distributed to the individual wells. To achieve the desired dosing accuracy, adjustable dosing valves are used, adapted for the chemicals in question here.
Prior art dosing valves are provided with accurately adjustable dosing devices and most often also with a flowmeter which allows the dosing amount to be monitored.
The chemicals used are a mixture of fluids, in which the greatest emphasis is laid on making the mixture have a desired chemical composition. Physical properties such as density and viscosity may vary between mixtures having the same chemical composition.
Thus, it is normal that the viscosity of the fluid is not known for the pressure and temperature conditions prevailing at the point of injection, and it is not a simple task either to predetermine the viscosity at the point of injection.
It has turned out that a change in viscosity of the fluid injected, results in a change in the injection flow even when sophisticated dosing valves according to prior art are used.
If restrictions are used, in which the flow is turbulent and thereby less sensitive to variations in the viscosity, it is a problem that the restriction becomes clogged as the restriction opening must be relatively small with the flow rates in question here.
The invention has as its object to remedy the drawbacks of the prior art.
The object is achieved, according to the invention, through the features set out in the description below and in the following Claims.